Triphasic Training Principle 35 – Concussion-induced Stability Deficit Principle
Preventing ACL Injuries After Concussion: How the 2IU Method, DSSS Testing, and Spring Ankle Torque Training Could Change the Game
The Concussion-ACL Connection: What the Data Reveals
A groundbreaking population-based study by the Mayo Clinic has revealed a compelling link between concussions and future ACL injuries. The research found that individuals who suffered a concussion had 1.6 times greater odds of sustaining an ACL injury within three years compared to those without a concussion history (2.4% vs. 1.5%). This risk was especially pronounced in males (OR = 2.0) and in athletes 16 years or younger (OR = 2.9).
The study supports earlier findings that concussions can impair neuromuscular control, leading to increased susceptibility to lower extremity injuries such as ACL tears. This is particularly concerning given that non-contact ACL injuries, which already account for a significant portion of these injuries, often result from compromised movement stability and neuromuscular dysfunction—exactly the types of issues that can follow a concussion.
Double Sling Stability System (DSSS): The Hidden Weak Link
Enter the Double Sling Stability System (DSSS), a framework that identifies and trains two critical muscular sling systems: the Spiral Sling and the Lateral Sling. These systems stabilize the body during complex athletic movements and are integral for efficient gait mechanics.
Coach Cal Dietz discovered that athletes with a concussion often exhibited dysfunction in these slings. Specifically, when using the Double Sling Stability System Test, he observed that the side opposite the concussion often showed poor activation—suggesting a neurologically induced imbalance. For instance, a right-side concussion often led to left-side sling weakness, affecting stability and increasing ACL risk.
This was a pivotal insight: the DSSS could be “off” long before a visible injury occurred.
The 2IU Method: A Breakthrough in Neuromuscular Reset
To counteract this instability, Dietz developed the 2IU Method (Double Inverted U Method)—a 30-second per leg activation protocol using a thumb or massage gun to reset neuromuscular function.
By activating the glute medius and tensor fasciae latae (TFL)—key parts of the lateral sling—and integrating them with the spiral sling, the 2IU Method effectively restores balance and lowers the risk of ACL injuries, especially in athletes recovering from concussions.
Importantly, early stabilization via the 2IU method was shown to be more effective if applied shortly after a concussion. While effects could fade quickly in acute cases, daily application—even twice daily—was shown to help maintain long-term stabilization.
Why Pre-Screening Matters: Real-Time Feedback for Real Injury Prevention
One of the most significant shifts in injury prevention philosophy has come from the implementation of real-time pre-testing and re-testing. Before introducing any new movement or rehab protocol, coaches are advised to test the athlete’s DSSS function, apply the 2IU activation, and retest.
Surprisingly, common recovery tools like foam rollers have been shown to temporarily deactivate the sling system for up to 6 hours. This makes testing crucial before and after any intervention to ensure that well-intended recovery work isn’t causing hidden damage.
Spring Ankle Torque Positions: The Foundation Beneath the Sling System
While the 2IU method and DSSS testing provide the upper framework for lower-body stability, Chris Korfist’s Spring Ankle System fortifies the base—starting from the foot and ankle. These positions (1 through 8) train athletes to stabilize and apply force efficiently, increasing proprioception, joint stability, and directional speed.
In particular the Spring ankle Torque positions:
Position One improves push-off and landing mechanics.
Position Two builds top-end sprint acceleration.
Position Three and Four develop lateral stability and agility, essential during directional changes.
Position Six and Seven enhance deep absorption and dynamic takeoff, ideal for jumping sports.
Position Eight sharpens impact absorption and propulsion, critical for all high-speed movement.
Incorporating these ankle torque positions into ACL rehab and return-to-play strategies helps reduce reinjury risk and improves movement quality from the ground up.
Conclusion: From Reactive to Proactive ACL Prevention
The future of ACL injury prevention lies in proactive, neuromechanically driven methods. The evidence is now clear:
Concussions significantly increase ACL injury risk, especially within three years.
The Double Sling Stability System, when tested and trained properly, can reveal critical imbalances.
The 2IU Method offers a fast, effective way to restore neuromuscular readiness.
Integrating Spring Ankle Torque Training enhances the entire kinetic chain.
By combining these systems, coaches, therapists, and athletes can move from reacting to ACL injuries to truly preventing them—even when the root cause begins with something as distant as a concussion.
Call to Action: If you’re a coach, trainer, or medical professional, start screening with the Double Sling Stability Test today. Integrate the 2IU Method and Spring Ankle Torque Positions into your programs. The data is undeniable—and your athletes’ futures may depend on it.
Peer-Reviewed Research on Concussion and ACL Injury Risk
McPherson, A. L., Shirley, M. B., Schilaty, N. D., Larson, D. R., & Hewett, T. E. (2020). Effect of a concussion on anterior cruciate ligament injury risk in a general population. Sports Medicine, 50(7), 1203–1210. https://doi.org/10.1007/s40279-020-01262-3123
National Guidelines for ACL Injury Prevention
National Athletic Trainers’ Association. (2018). National Athletic Trainers’ Association position statement: Prevention of anterior cruciate ligament injury. Journal of Athletic Training, 53(1), 5–19. https://doi.org/10.4085/1062-6050-99-164
Triphasic Training Concepts and Methods
Dietz, C. (2025, May 12). Preventing ACL non-contact injuries with 2IU method. Triphasic Training. https://triphasictraining.com/preventing-acl-non-contact-injuries-with-2iu-method/5
Dietz, C. (2025, May 19). Non-contact ACL injuries: The double system failure. Triphasic Training. https://triphasictraining.com/non-contact-acl-injuries/6
Dietz, C. (2024, July 23). The non-contact ACL solution [Online course]. Triphasic Training. https://triphasictraining.thinkific.com/products/courses/Aclnoncontact7
Korfist/Dietz, C. (2024, June 22). Exploring the power of spring ankle torque positions. Triphasic Training. https://triphasictraining.com/exploring-the-power-of-spring-ankle-torque-positions/
